1. Field of the Invention
The present invention relates to a method for producing a particulate zeolite and a particulate zeolite produced by the method. More particularly, the present invention is concerned with a method for producing a particulate zeolite in a slurry form or in an isolated form, in which a nucleating slurry is mixed with a first raw material mixture and heated to obtain a precursory slurry mixture and subsequently the precursory slurry mixture is mixed with a second raw material mixture and heated to obtain a product slurry. Also, the present invention is concerned with fine particles of a zeolite in a slurry form or in an isolated form, produced by the above-mentioned method. The produced zeolite exhibits in a dry solid form peaks ascribed to interplanar spacings of 11.1.+-.0.2, 10.1.+-.0.2, 3.85.+-.0.07, 3.74.+-.0.05 and 3.72.+-.0.05 angstroms in an X-ray powder diffraction pattern, which are characteristic of zeolites of the ZSM-5 family.
The particulate zeolite is widely utilized as for example, an adsorbent, a catalyst, a molecular sieve, an agent for soil improvement, a filler for paper and an agent for waste water treatment.
2. Discussion of Related Art
ZSM-5 is a synthetic zeolite developed by Mobil Oil Corporation, N.Y., the United States (see U.S. Pat. No. 3,702,886). Initially, ZSM-5 was synthesized by performing crystallization from a raw material mixture comprised of silica, alumina, an alkali metal, a tetrapropylammonium salt and water. Thereafter, proposals were made to use a cheaper substitute material for the tetrapropylammonium salt which is very expensive. As a substitute material, an alcohol was proposed in Japanese Patent Application Laid-Open Specification No. 52-43800/1977, a lower alkyl urea was proposed in Japanese Patent Application Laid-Open Specification No. 61-68319/1986, and an aminoalcohol was proposed in Japanese Patent Application Laid-Open Specification No. 57-7818/1982.
Further, various proposals were made for producing ZSM-5 zeolites by the use of ZSM-5 seeds. In U.S. Pat. No. 4,175,114, ZSM-5 seeds were employed to decrease the amount of expensive tetrapropylammonium salt. In Japanese Patent Application Publication Specification No. 61-59246/1986, ZSM-5 seeds were employed in place of the expensive tetrapropylammonium salt. In Japanese Patent Application Laid-Open Specification Nos. 60-71519/1985 and 60-77123/1985, ZSM-5 seeds were partly recycled. These proposals have a drawback in that it is difficult to produce fine particles of ZSM-5 zeolites.
Still further, various proposals were made for producing fine particles of ZSM-5 zeolites. In Japanese Patent Application Laid-Open Specification No. 56-54222/1981, strong agitation was carried out during crystallization, without the use of seeds, to obtain fine particles of ZSM-5 zeolites. In Japanese Patent Application Laid-Open Specification No. 50-5335/1975, aging was performed by allowing a pre-crystallization mixture of ZSM-5 to stand still at a temperature of from 90.degree. to 110.degree. C. for a period of several days to thereby obtain fine particles of ZSM-5 zeolites. These proposals have a drawback in that operations are not easy, causing reproducibility to be poor.
Moreover, in Japanese Patent Application Laid-Open Specification No. 61-58812/1986, it was proposed to employ a method in which first a raw material mixture containing no organic cation is crystallized to obtain a crystalline aluminosilicate powder exhibiting a specific X-ray diffraction pattern, and subsequently particulate ZSM-5 is synthesized in the presence of an organic cation using the powder as ZSM-5 seeds. This proposal has a drawback in that separation of alumino-silicate powder is required, which is not easy.
The present inventors previously proposed a method for producing particulate ZSM-5 as disclosed in Japanese Patent Application Laid-Open Specification No. 63-315512/1988, in which first a precursory slurry mixture containing ZSM-5 having a low crystallinity is produced in the presence of an organic material of a lower alkyl urea, and subsequently the precursory slurry mixture is mixed with a raw material mixture, followed by heating to effect a hydrothermal reaction of the mixture of the raw material mixture and the precursory slurry mixture. Further, the present inventors previously proposed another method for producing particulate ZSM-5 as disclosed in Japanese Patent Application Laid-Open Specification No. 1-180835/1989, in which first a precursory slurry mixture containing semicrystalline ZSM-5 is produced in the absence of an organic material, and subsequently the precursory slurry mixture is mixed with a raw material mixture, followed by heating to effect a hydrothermal reaction of the mixture of the raw material mixture and the precursory slurry mixture. These proposals have a drawback in that control of crystallization of the formed zeolite is difficult, so that desired particulate ZSM-5 cannot be produced with high reproducibility.
The zeolites of the ZSM-5 family exhibiting peaks ascribed to interplanar spacings of 11.1.+-.0.2, 101.+-.0.2, 3.85.+-.0.07, 3.74.+-.0.05 and 3.72.+-.0.05 angstroms in an X-ray powder diffraction pattern are not limited to the above zeolites, and include other various zeolites, such as ZSM-8 zeolite disclosed in German Patent No. 2,049,755, ZETA-1 zeolite disclosed in German Patent No. 2,548,697, ZETA-3 zeolite disclosed in U.K. Patent No. 1,553,209, NU-4 zeolite disclosed in German Patent No. 3,268,503, NU-5 zeolite disclosed in German Patent No. 3,169,606, TZ-01 zeolite disclosed in U.S. Pat. No. 4,581,216, crystalline aluminosilicate disclosed in U.S. Pat. No. 4,954,326, TRS zeolite disclosed in German Patent No. 2,924,870, MB-28 zeolite disclosed in European Patent No. 21,445, TSZ zeolite disclosed in Japanese Patent Application Laid-Open Specification No. 58-45111/1983 and AZ-1 zeolite disclosed in European Patent No. 113,116.
As described above, various proposals have been made for producing zeolites of the family of ZSM-5. However, there is still a strong demand for a method by which a zeolite of the ZSM-5 family zeolite in a finely particulate form is efficiently produced with high reproducibility.